Based on further discussions with the folks administering the onestream environment, this was something they did wrong.
Unfortunately, I have no clue what they did wrong since they didn't tell me. I'm guessing it was something simple, like they forgot to actually grant the user access to this particular application. Either way, I don't think it was a "normal" authentication failure, or the error from the REST api would have been an HTTP status (401 or whatever).
The error message from the product leaves a lot to be desired. Assuming the administrator of onestream can misconfigure a user in a simple way, we should then get a simple error message back to tell us about it. The current one ("unable to create database connection") is way too technical; it probably assumes we have access to the underlying source code for the sake of further investigation.
